Re: [NTLK] Recharging a dead vs. low battery

From: Scott Clitheroe (scott_at_clitheroe.ca)
Date: Wed Mar 19 2003 - 18:11:24 PST


Be careful how you define "fully drained" when you are talking about NiCad
battery packs. No two cells in any pack are exactly identical in their
capacity and discharge characteristics, and as a result, discharging a pack
too low results in one or more cells going below their nominal (dead)
voltage levels. When this happens to a NiCad cell (or any rechargeable
cell, for that matter), you cause a slight, but permanent amount of damage
(actual chemical and physical changes occur in the cell), which will further
alter the characteristics of the cell the next time it is charged and
discharged, accelerating the wear on the cell down the road. The end result
is that the pack becomes "mismatched", and every time you cycle the pack
(charge it up, and discharge it), some cells are dying prematurely on the
discharge side, and some cells are getting overcharged on the charge side of
the cycle (because they still had a partial charge, despite the pack
appearing low in voltage). Both overcharging and over-draining cells are
the leading causes of NiCad failure.

While the memory effect is certainly a concern, you will do more harm in the
long run taking a pack below 10-15% consistently, in my opinion.

As an aside for pack builders out there, you shouldn't be buying cells four
at a time to assemble packs. You should be buying them 8, or even 16 at a
time, charging them, connecting them to a moderate resistive load, and
measuring the time it takes them to hit their rated minimum voltage using a
volt meter. Then assemble packs out of the cells that perform most closely.
You'll be rewarded with packs that last longer, and you'll get more charge
cycles out of them. And that's not just my opinion, that is fact.

Thanks for taking the time to read,
Scott

----- Original Message -----
From: "Nathan Turnage" <nturnage_at_andadv.com>
To: <newtontalk_at_newtontalk.net>
Sent: Wednesday, March 19, 2003 3:19 PM
Subject: Re: [NTLK] Recharging a dead vs. low battery

> No, the battery on the Newton 2x00 does not have a memory. The Ni-Cad
> (nickel cadmium) batteries in the 1x0 models did have a memory and had
> to be fully drained before being charged. However, the 2x00s use NiMH
> (nickel metal hydride0 batteries that don't suffer the same problems.
>
>
> Nathan Turnage
> [the new(t) guy]
>
>
>
> Chris Searles wrote:
> > Does it make a big difference for the battery life of the rechargeable
> > battery in a Newton 2100 if you wait till the battery dies before
recharging
> > or if you try to recharge when the battery level goes no lower than,
say,
> > 20%?
> >
> > chris searles
> >
>
>
> --
> This is the NewtonTalk list - http://www.newtontalk.net/ for all inquiries
> List FAQ/Etiquette/Terms: http://www.newtontalk.net/faq.html
> Official Newton FAQ: http://www.chuma.org/newton/faq/
>
>

-- 
This is the NewtonTalk list - http://www.newtontalk.net/ for all inquiries
List FAQ/Etiquette/Terms: http://www.newtontalk.net/faq.html
Official Newton FAQ: http://www.chuma.org/newton/faq/


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